Thank you, John and bakerchj.
Naturally, when something goes wrong like this, you wonder whether there is something deeper wrong in your own computer. We can rule that out. I imagine more people will be reporting the problem.
As I mentioned, I installed IE 9, but I used the web search after that. There was a Vista update (and probably the same update for other OS's) last Tuesday on account of the false certificates. Maybe that did it. I didn't try to use the search function till Friday.